Thanks for all your insightful comments and recommendations.
Roman and Juraj,
I've used kentico's default saving. All the editable region have it's own unique ID, i.e Card1, Card2, and Card3.
Why don't you add those editable text one by one to the page template without wrapping them into a single web part?
Initially, I wanted the user to fill-up the content by just typing the contents in the editable boxes, without thinking about the layout and other settings. Let's say this user is really old non-technical. I don't want them to drag and drop webparts all over the template or give the freedom to control the layout because this will lead to more problem.
Upon reading Mike and Brendan's (for the second time) comments, i've decided to revert to the plain old webpart, where the user will open the design tab and manually enter the contents.
Thanks for sharing your presentation. Just wondering if you have a full video presentation of this?